The invention relates generally to electromagnetic valves, and in particular, to electro-magnetic valves having a very fast response and a favorable temperature-gradient characteristic which are suitable for use in an electronic fuel-injection system for an internal combustion engine.
Similar electromagnetic valves are well known. They are utilized, for example, in electronic fuel-injection systems, in which a temperature compensating resistance is connected in series with each magnetic valve. In this type of circuit, the winding of the electro-magnetic valve typically has a resistance of 2.35 ohms, and the compensating resistor typically has a resistance of 6 ohms. This well-known arrangement possesses the advantage of having a fast response, and a low temperature-rise, of the magnetic coil, because only a small portion of the total electrical energy transformed into heat in the magnetic winding and in the compensating resistor takes place in the valve.
If, in addition, the compensating resistor is made of constantan, the combined resistance (the resistance of the magnetic coil plus the compensating resistance) yields favorable temperature-gradient characteristics. However, this method of construction entails the disadvantage that the constantan compensating resistor is very expensive because it is a precision component, and because it has a very high power-consumption.